FIGS. 1A through 1C of the accompanying drawings show a structure of a balanced vane-type hydraulic motor. FIG. 1A is a schematic cross-sectional view taken along line IA-IA of FIG. 1B, FIG. 1B is a schematic cross-sectional view taken along line IB-IB of FIG. 1A, and FIG. 1C is a plan view showing a part of a cam casing 280 as viewed from above.
As shown in FIGS. 1A through 1C, the balanced vane-type hydraulic motor comprises a rotor 290 rotatably housed in a rotor-housing chamber 286 formed in a cam casing 280, a plurality of vanes 295 inserted in the rotor 290 and held in contact with an inner surface of the rotor-housing chamber 286, a front cover 300 and an end cover 310 for covering opposite sides of the rotor 290 and the vanes 295, and a main shaft 320 fixed to the rotor 290 and rotatably supported by bearings 301, 311 mounted respectively in the front cover 300 and the end cover 310. The cam casing 280 has a supply port 281 defined therein for supplying a pressurized fluid (i.e. a working fluid comprising a low-viscosity fluid such as water) into the rotor-housing chamber 286 of the cam casing 280. The cam casing 280 also has a return port 283 defined therein for discharging the fluid which has been supplied into the rotor-housing chamber 286. The supply port 281 and the return port 283 are connected to the rotor-housing chamber 286 through a fluid path (fluid-supply path) 282 and a fluid path (fluid-return path) 284, respectively.
When the pressurized fluid (working fluid) flows from the supply port 281 to the rotor-housing chamber 286, the pressurized fluid (working fluid) acts on the vanes 295 projecting from the rotor 290 to generate a torque, thereby rotating the rotor 290. After rotating the rotor 290, the working fluid is discharged from the return port 283.
In the balanced vane-type hydraulic motor using a low-viscosity fluid such as water as the working fluid, a bypass path 285 is provided to return the working fluid, that has leaked through the bearings 301, 311 provided on both sides of the rotor 290, to the return port 283, which is a low-pressure side. The working fluid in the rotor-housing chamber 286, which is a high-pressure side, passes through both side clearances (a gap between the rotor 290 and the front cover 300 and a gap between the rotor 290 and the end cover 310) S and gaps between the main shaft 340 and the bearings 301, 311, and is then led to the return port 283 through the bypass path 285. With this arrangement, the following advantages are obtained:
(1) The pressures applied to the both side surfaces of the rotor 290 are substantially equal to the pressure in the return port 283, and thus are held in a state of balance. Therefore, essentially no pressure acts on the rotor 290 in the thrust direction (the extending direction of the main shaft 320). The rotor 290 is balanced in the cam casing 280 in the thrust direction, thus making it possible to reduce the frictional loss (torque loss) due to the sliding motion between the rotor 290 and each of the front cover 300 and the end cover 310.
(2) Since the working fluid is led to the bearings 301, 311, the bearings 301, 311 can be prevented from being deteriorated even if the working fluid comprises a low-viscosity fluid such as water. Thus, the durability of the main shaft 320 and the bearings 301, 311 can be increased.
(3) Since an internal seal pressure P is small and the shaft seal 330 applies a small pressing force against the main shaft 320, no friction-induced mechanical loss is generated in this shaft seal region. In addition, the shaft seal 330 and the main shaft 320 do not suffer frictional wear, thus increasing the durability thereof.
(4) No liquid reservoir is formed around the bearings 301, 311, and the working fluid around the bearings 301, 311 circulates at all times. Therefore, the working fluid is prevented from being rotted and microorganisms are prevented from being produced in those regions.
A rotary actuator such as the above vane-type hydraulic motor is utilized in various kinds of apparatuses, and hence an output shaft (main shaft) of the rotary actuator is required to be rotated in one direction, the opposite direction, or the both directions depending on the operational conditions of the rotary actuator.
Generally, in the hydraulic motor, it is required to provide a pipe for supplying a pressurized fluid to actuate the hydraulic motor and another pipe for discharging the fluid from the hydraulic motor. The hydraulic motor has a supply port and a return port as a connection port for connecting the above pipes. In the vane-type hydraulic motor shown in FIGS. 1A through 1C, the supply port 281 and the return port 283 are provided in the cam casing 280.
In FIG. 1B, in the case where the hydraulic motor is rotated in the direction indicated by the arrow (i.e. the clockwise direction), piping is arranged such that the left port in FIG. 1B is used as the supply port 281 and the right port is used as the return port 283. Therefore, the hydraulic motor is assembled using a component serving as the cam casing 280 which has the right port (return port) 283 and the bypass path 285 communicating with each other as shown in FIG. 1B.
On the other hand, in the case where the hydraulic motor is rotated in the direction opposite to the direction indicated by the arrow shown in FIG. 1B (i.e. the counterclockwise direction), the right port in FIG. 1B is used as the supply port and the left port is used as the return port. Therefore, it is required to assemble the hydraulic motor using a component serving as the cam casing 280 which has a left port and a bypass path communicating with each other, unlike the component shown in FIG. 1B.
If the hydraulic motor is constructed such that the working fluid is supplied from the return port 283 shown in FIG. 1B and is discharged from the supply port 281 shown in FIG. 1B, then the internal seal pressure P is increased. Consequently, the damage to the shaft seal 330 or the wear on the main shaft 320 will be accelerated, and the durability of the shaft seal 330 will be deteriorated. Further, the effect of the bypass path 285 will be lowered, and other problems will arise. As a result, the hydraulic motor will fail to perform its function.
Consequently, the balanced vane-type hydraulic motor needs to have different components prepared for the respective rotational directions of the motor, and hence the manufacturing cost is increased.